samples/bpf: bpf_load.c order of prog_fd[] should correspond with ELF order (7bc57950) · Commits · 戴 / test

An eBPF ELF file generated with LLVM can contain several program section, which can be used for bpf tail calls. The bpf prog file descriptors are accessible via array prog_fd[]. At-least XDP samples assume ordering, and uses prog_fd[0] is the main XDP program to attach. The actual order of array prog_fd[] depend on whether or not a bpf program section is referencing any maps or not. Not using a map result in being loaded/processed after all other prog section. Thus, this can lead to some very strange and hard to debug situation, as the user can only see a FD and cannot correlated that with the ELF section name. The fix is rather simple, and even removes duplicate memcmp code. Simply load program sections as the last step, instead of load_and_attach while processing the relocation section. When working with tail calls, it become even more essential that the order of prog_fd[] is consistant, like the current dependency of the map_fd[] order. Signed-off-by:

Jesper Dangaard Brouer <brouer@redhat.com> Acked-by:

Alexei Starovoitov <ast@kernel.org> Signed-off-by:

David S. Miller <davem@davemloft.net>

samples/bpf/bpf_load.c

+5 −14

Original line number	Diff line number	Diff line
		@@ -516,16 +516,18 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
		processed_sec[maps_shndx] = true;
		}

		/* load programs that need map fixup (relocations) */
		/* process all relo sections, and rewrite bpf insns for maps */
		for (i = 1; i < ehdr.e_shnum; i++) {
		if (processed_sec[i])
		continue;

		if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
		continue;

		if (shdr.sh_type == SHT_REL) {
		struct bpf_insn *insns;

		/* locate prog sec that need map fixup (relocations) */
		if (get_sec(elf, shdr.sh_info, &ehdr, &shname_prog,
		&shdr_prog, &data_prog))
		continue;
		@@ -535,26 +537,15 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
		continue;

		insns = (struct bpf_insn *) data_prog->d_buf;

		processed_sec[shdr.sh_info] = true;
		processed_sec[i] = true;
		processed_sec[i] = true; /* relo section */

		if (parse_relo_and_apply(data, symbols, &shdr, insns,
		map_data, nr_maps))
		continue;

		if (memcmp(shname_prog, "kprobe/", 7) == 0 \|\|
		memcmp(shname_prog, "kretprobe/", 10) == 0 \|\|
		memcmp(shname_prog, "tracepoint/", 11) == 0 \|\|
		memcmp(shname_prog, "xdp", 3) == 0 \|\|
		memcmp(shname_prog, "perf_event", 10) == 0 \|\|
		memcmp(shname_prog, "socket", 6) == 0 \|\|
		memcmp(shname_prog, "cgroup/", 7) == 0)
		load_and_attach(shname_prog, insns, data_prog->d_size);
		}
		}

		/* load programs that don't use maps */
		/* load programs */
		for (i = 1; i < ehdr.e_shnum; i++) {

		if (processed_sec[i])

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